Diesel engines are operated at higher than stoichiometric air to fuel mass ratios for improved fuel economy. Such lean-burning engines produce a hot exhaust with a relatively high content of oxygen and nitrogen oxides (NOx). The temperature of the exhaust from a warmed up diesel engine is typically in the range of about 200° C. to about 400° C. and has a representative composition, by volume, of about 10% to about 17% oxygen, about 3% carbon dioxide, about 0.1% carbon monoxide, about 180 parts per million (ppm) hydrocarbons, about 235 ppm NOx and the balance nitrogen and water.
These NOx gases, typically comprising nitric oxide (NO) and nitrogen dioxide (NO2) are difficult to reduce to nitrogen (N2) because of the high oxygen (O2) content in the hot exhaust stream. Existing NOx reduction technologies, such as lean NOx trap technology (LNT) and urea/SCR technology, can provide some suitable NOx reduction performance under certain conditions. However, both LNT and urea/SCR technologies have their inherent drawbacks. For example, the LNT technology requires a large amount of noble metal catalysts and a sophisticated engine control technology, while the urea/SCR technology requires an onboard urea tank as well as a urea distribution infrastructure.
Methods to reduce these NOx gases include, for example, U.S. Pat. No. 6,936,562 of Byong Kwon Cho et al., entitled “Hydrothermally Stable Catalyst for Improved Lean NOx Reduction,” which is hereby incorporated by reference herein in its entirety, which describes in the abstract certain metal-exchanged SUZ-4 zeolites that have catalytic activity for the reduction of NOx in the exhaust of a hydrocarbon or alcohol fueled engine operated under fuel lean conditions. Initially the SUZ-4 zeolite contains alkali metal cations such as Li+, Na+, K+ and/or Cs+. These alkali metal cation-containing zeolites are partially exchanged with at least one of copper (II), silver (I), iron (III) or cobalt (II) ions. The resulting partially exchanged SUZ-4 zeolites display such activity and are stable under extreme hydrothermal aging conditions. See also U.S. Pat. No. 6,645,448 of Byong Kwon Cho et al., entitled “Hydrothermally Stable Catalyst for Improved Lean NOx Reduction,” which is hereby incorporated by reference herein in its entirety.
U.S. Pat. No. 6,957,528 of Byong Kwon Cho, entitled “NO Reduction With Diesel Fuel Reformed by Nonthermal Hyperplasma,” which is hereby incorporated by reference herein in its entirety, describes in the abstract the reduction of NOx in diesel engine exhaust gas, typically at about 200° C. to 400° C., accomplished using a dual bed NaY—CuY zeolite reduction catalyst. The effectiveness of the catalyst in reducing the nitrogen oxides is markedly increased by the separate and sequential additions of plasma-reformed diesel fuel and ozone to the exhaust before it contacts the powdered catalyst. Reformed diesel fuel is obtained by withdrawing fuel from on-board storage, heating the withdrawn volume and stripping a more volatile fraction with air and passing the air/volatile diesel fuel fraction through a non-thermal plasma reactor. Ozone is obtained by blowing ambient air through a second non-thermal plasma reactor.
Illustrated in U.S. Pat. No. 7,093,429 of Byong Kwon Cho, entitled ‘Reforming Diesel Fuel for NOx Reduction,’ the disclosure of which is totally incorporated herein by reference, is, in embodiments, a method of using diesel fuel in the selective catalytic reduction (SCR) of NOx where the diesel fuel is fractionated and reformed by an air-plasma stream from an efficient nonthermal plasma generator.
Illustrated in U.S. patent application Ser. No. 11/155,179, of Byong Kwon Cho et al., filed on Jun. 17, 2005, entitled ‘Continuous Reforming of Diesel Fuel for NOx Reduction,’ the disclosure of which is totally incorporated herein by reference, describes, in embodiments, a method and equipment for continuous fractionation and reformation of diesel fuel with air plasma to produce partially oxygenated hydrocarbons for NOx reduction.
Illustrated in U.S. Pat. No. 7,090,811 of Byong Kwon Cho et al., entitled ‘Method of Reducing NOx in Diesel Engine Exhaust,’ the disclosure of which is totally incorporated herein by reference, is, in embodiments, a method of reducing NOx content in diesel engine exhaust using ethanol as the reductant for selective catalytic reduction of NOx.
The appropriate components and process aspects of each of the foregoing U.S. Patents and Applications may be selected for the present disclosure in embodiments thereof.